Propolis is resinous and contains a complex mixture of substances collected by honeybees. Propolis has a color varying from greenish yellow to dark brown. Bees use propolis to seal holes in their hives, exclude draught, protect against external invaders and mummify the carcasses of predators. The amount of propolis available from a bee colony is related to the hive structure used in the honey and pollen gathering operations.
Bees collect resins from numerous different plant species, thus the chemical composition of propolis varies greatly and depends directly on the local flora and phenology of the host plants and indirectly on the locality and time of collection. It is believed that part of the substances collected undergoes chemical alteration by bee enzymes prior to incorporation in propolis, making propolis a substance considered to be of both plant and animal origin. Specifically, bees mix the plant exudates (including resins, waxes and oils collected from different parts of plants and trees including branches, flowers, pollen and buds) with beeswax (which bees secrete through glands located near the hypopharygeal region of the bees' bodies) and β-glucosidase they secrete during plant exudate collection and small amounts of sugar, which results in whole propolis. Due to differences in chemical composition, the biological activity of propolis also differs with the geographic area.
Propolis is collected and sold, but methods of preparation and the resulting product vary considerably. In most countries, tinctures of propolis are the most common form of propolis available to consumers.
While chemical composition varies, propolis is generally composed of about 45% resin, 35% wax and 20% inert material. More specifically, propolis constituents include about 10% essential oils, 5% pollen, and 15% various organic polyphenolic compounds including, flavonoids and phenolic acids. Propolis is most often purified-by extraction with solvents, particularly ethanolic extracts of propolis. The extraction process removes the wax and the inert material, and preserves the resinous phenolic fraction. A multi-step extraction with ethanol can result in dewaxed propolis extracts rich in polyphenolic components.
There is substantial evidence that propolis has antiseptic, antifungal, antibacterial, antiviral, anti-inflammatory and antioxidant properties. The polyphenolic content of propolis is considered to contribute more to the observed healing effects than other propolis constituents. Propolis has a long history of use in folk medicine.
Alcohols, aldehydes, aliphatic and aromatic acids, aliphatic and aromatic esters, chalcones, terpenoids, steroids, sugars, amino acids as well as large numbers of flavonoids have been identified in propolis. The flavonoids, aromatic acids and phenolic derivatives are believed to be the main components having therapeutic effects with flavonoids and phenolic acid esters, being known for their antibacterial and antioxidant properties.
Intact propolis, however, is not useful in food products because it generally contains large amounts of contaminants and is barely soluble in water. Currently, propolis is added in the form of extracts to food and health care products. Because the resin portion of whole propolis contains most of the polyphenolic compounds, commercially it has been desirous to obtain resin extracts from which the polyphenolic compounds are further extracted, with the less desirous wax portion becoming the waste product. Up until now, there has been no use for the wax portion of propolis and thus it remains as the waste product of refined propolis.